Sorry hopefully my statement is not going to turn out true but by the time you find your solution, if its really brooks your clown up lorry le.
If not, since you are still in the unsure stage of what your fish is suffering,
1.then you can freshwater dip it to give yourself some time to find a permanent solution.
If your clownfish is in QT then good. If not you have to separate it for treatment including any other clowns that was in the tank with it.
Your best bet is at C328 + Polyart. See if they got stock the following meds :
2. I noticed you're finding for formalin 37%. I am not sure where you can get it.
3. Last time still have Interpet 7 - good cure for brooks. now I am not sure. try asking see if got very old stock.
4. If cannot find, try finding Waterlife Sterazin - its a combo treatment of formaldehyde & malachite green. formaldehyde is actually the base of formalin without the ethyl alcohol. but its way way milder.
4. If cannot find Waterlife Sterazin, find amongst bottles that has this ingredient.
5. If still cannot find, look for Quinine Sulfate as an ingredient.
If all above you cannot find, then you have to wait for other bros to chime in or your clown to up lorry, whichever is faster. (suspect clown go first if its really brooks).
Good luck.